As is known in the art, Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays. UV light includes wavelengths in the range of 100 to 400 nanometers (nm) and energies from 3 to 124 electron-volts. UV light is emitted by the Sun, electric arcs, and artificial light sources such as black lights. As an ionizing radiation, UV sources can cause chemical reactions that cause many substances to glow or fluoresce. Although UV light is beyond visible light, most people are aware of the effects of UV radiation through sunburn. However, the UV spectrum has many other effects, both beneficial and damaging, on human health.
UV radiation can be classified in a number of ways, including as bands of radiation separated into the following:
UV A-band: 400-320 nm.
UV B-band: 320-280 nm.
UV C-band: 280-200 nm.
The Sun emits UV A, UV B, and UV C-band radiation; however, the Earth atmosphere's ozone layer absorbs about 98.7% of this radiation, primarily in the UV B and UV C-bands. Other natural sources of UV radiation include lightning and fires.
As is also know in the art, ordinary glass is partially transparent to UV A-band radiation, but is opaque to shorter UV wavelengths in the UV B and UV C-bands. Silica or Quartz glass, depending on quality of materials, can be transparent to even UV C-band radiation, while window glass passes about 90% of UV light above 350 nm, but blocks over 90% of UV light below 300 nm.
UV radiation can be an effective viricide and bactericide and is used in wastewater treatment. However, it is only beginning to find usage in drinking water sterilization. UV lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. In particular, UV light can be an effective germicide because it can prohibit reproduction by damaging cellular DNA, even though it may not kill a host organism.
As is also known in the art, UV C-band radiation is invisible to humans and to ordinary cameras, video gear, and night vision systems. Existing UV detectors generally include either solid-state devices, such as a silicon carbide or aluminum nitride device, or gas-filled tubes as sensing elements. UV detectors are primary used for detecting artificial light. For example, the petrochemical industry uses UV detectors to monitor burning hydrogen flames which radiate strongly in the 185-260 nm range. UV detectors are sensitive to burning compounds, such as hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Industrial safety applications employ UV detectors to effectively detect arc-welding, electrical arcs, lighting, and X-rays.
UV C-band detectors are solar blind, since the Earth's atmosphere blocks solar UV C-band radiation, which makes them useful for both indoor and outdoor applications. Furthermore, UV C-band detectors are generally unaffected by night, rain, fog, and dusty environments. Another useful feature is that UV C-band radiation reflects well off soil, pavement, and other manmade surfaces, as well as water. One type of UV C-band detector is a UV C-band camera that includes components such as an image intensifier tube and charge-coupled device (CCD). The tube intensifies electromagnetic energy by converting photons into electrons that dislodge other electrons to produce “intensified” energy captured by the CCD.